The Evolved Packet System (EPS) in the 3rd Generation Partnership Project (3GPP) consists of Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Mobility Management Entity (MME), Serving Gateway (S-GW), Packet Data Network Gateway (PDN GW, also referred to as P-GW), and Home Subscriber Server (HSS).
The EPS supports interworking with the non-3GPP system, as shown in FIG. 1, wherein, the interworking with the non-3GPP system is implemented with the S2a/b/c interface, and the PDN GW works as an anchor point between the 3GPP system and the non-3GPP system. In the EPS system architectural diagram, the non-3GPP system access is divided into untrusted non-3GPP access and trusted non-3GPP access; wherein the untrusted non-3GPP access needs to go through the evolved packet data gateway (ePDG) in order to connect with the PDN GW, the interface between the ePDG and the PDN GW is S2b; the trusted non-3GPP access can directly connect with the PDN GW through the S2a interface, and the S2a interface uses the Proxy Mobile Internet Protocol (PMIP) for information exchange; in addition, the S2c interface provides user plane related control and mobility support between the User Equipment (UE) and the PDN GW, and its supporting mobility management protocol is the Mobile IPv6 Support for Dual Stack Hosts and Routers (DSMIPv6), which can be used for both the untrusted non-3GPP access and the trusted non-3GPP access.
The Wireless Local Area Network (WLAN) can be used as a non-3GPP system to access to the Evolved Packet Core (EPC), and this involves a lot of interconnection issues of the fixed mobile convergence that are concerned by many operators.
Currently, there is a lot of study on the process and policy interoperability of the S2b interface and the S2c interface, but there is little study on the S2a interface. The Study on S2a Mobility based On GTP & WLAN access to EPC (SaMOG) is mainly to study the interconnection problem in the case that the WLAN works as a trusted non-3GPP IP access network (TNAN) and the UE accesses to the EPC through the S2a interface. In the related art, as shown in FIG. 2, there are primarily two modes for the process of the UE accessing to the 3GPP EPC through the non-3GPP access network if differentiating according to how to trigger the non-3GPP access network to initiate a tunnel establishment to the PDN GW, and the two modes are specifically described as follows:
mode one: after the UE completes the non-3GPP specific process and the Extensible Authentication Protocol (EAP) authentication process, the Layer 3 (L3) message is executed between the UE and the TNAN network element, then after the TNAN receives the L3 message, it initiates a tunnel establishment process to the PDN GW of the mobile core network.
Mode two: besides of the L3 messages, the Layer 2 (L2) messages such as the EAP messages can also be used as a triggering mode. After the UE completes the non-3GPP specific process and the EAP authentication process, and after the TNAN receives the EAP authentication success message, it initiates a tunnel establishment process to the PDN GW of the mobile core network.
The research scheme of the SaMOG is divided into scheme that has no effect on the UE and scheme that has an effect on the UE. The so-called scheme having no effect on the UE means that the UE does not support transmitting the Access Point Name (APN) information, additional Packet Data Network (PDN) connection, as well as the handover process between the access systems, and so on, and such a UE corresponds to the UE prior to the Release 11 (R11) of the 3GPP standards, and is referred to as R11 UE hereinafter; while the scheme having an effect on the UE refers to that the UE supports transmitting the APN information, the additional PDN connection, as well as the handover process between the access systems, and so on, such a UE corresponds to the UE in the Release 12 (R12) of the 3GPP standard, and is hereinafter referred to as R12 UE; in the related art, a specific implementation to ensure the UE subsequently performing a seamless handover between the access systems is as follows: when the UE first accesses to the 3GPP system or the non-3GPP system, after it selects the PDN GW, the PDN GW needs to update the PDN GW identity to the HSS; then, when the UE switches, the target access system of the handover acquires the previously saved PDN GW identity from the HSS. Moreover, if the PDN GW identity that is saved by the HSS and associated with the same APN is to be updated, the HSS updates the PDN GW identity to the MME or to the non-3GPP network element via the AAA server.
For the scheme having no effect on the UE, although the UE does not support the handover procedure, it can independently access to the 3GPP core network via the WLAN access system and the 3GPP access system simultaneously; moreover, the UE may use the same APN, but access to different PDN GWs. In the related art, if the PDN GW does not receive a handover indication form the UE, it considers that both of the different accesses are the first access of the UE, therefore when the UE first accesses via the WLAN access system, the PDN GW updates the PDN GW identity to the HSS; then, when the UE accesses via the 3GPP access system, the PDN GW updates the PDN GW identity to the HSS again, at this time, the new PDN GW identity overwrites the previously saved PDN GW identity; moreover, the HSS finds out that the PDN GW identity selected by the UE based on the same APN changes, and it sends the updated PDN GW identity to the access gateway of the WLAN via the AAA server, in turn, this causes an exception process in the WLAN network; whereas, when the UE accesses via the 3GPP access system firstly and later accesses via the WLAN access system, the HSS finds out that the PDN GW identity selected by the UE based on the same APN changes, it sends the changed PDN GW identity to the MME, in turn, this causes an exception process in the 3GPP network.
In addition, the Universal Mobile Telecommunications System (UMTS) also support interworking with the non-3GPP system; the difference is, the Serving General Packet Radio Service Support Node (SGSN) is used to replace the MME and the S-GW, and the Gateway General Packet Radio Service Supporting Node (GGSN) is used to replace the P-GW.
Therefore, the problem of the UE that does not support the handover accessing to the mobile core network via the UMTS and the non-3GPP system simultaneously also exists.